Chaps,
1. As p3asa's excellent video explains its pointless to assume a car will run better on high octane fuel. Unless the compression ratio is changed it won't matter.
2. There might, however, be other benefits.
3. As John and others have pointed out its often hard to see any difference suggesting if there is one its small.
However,
4.
http://www.pistonheads.com/gassing/topic.asp?t=302977 demonstrated on some cars with VVT improvements are seen scientifically. The new mk7 GTI is the first GTI with VVT so comparisons with mk5/6 don't apply, it's a different engine.
5.
http://www.golfgtiforum.co.uk/index.php?topic=256725.msg2357665#msg2357665 suggests fuel economy and power should be up with the EA888 using high octane.
6. Remaps may or may not mean the fuel should be changed, depends on the compression ratio post remap.
7. It's gonna be hard to prove as we'd need large sample sizes to overcome variations due to driving style etc... Obviously we'll all have our opinions and will act on them but for proof we need more than 1 data point.
I guess a bunch of us using v-power or something could compare stats to a bunch on regular fuel. Or we could all just do what we want and forget about it.
EDIT: forgot my conclusion...
The mk7 should benefit from high octane fuel
in theory. There is little value using data based on other cars, you've got to look at the mk7 itself as its engine setup and ECU behaviour is specific to it. We can't prove the theory is correct without lots of data points, but we also can't just assume any benefits exist.
